The present invention relates to a method for laying a foundation for an existing building structure, said method comprising establishment of a distance between a foundation of the building structure and a foundation pile with an upper pan providing a carrier surface on the foundation pile and establishment of a core between the carrier surface on the foundation pile and a carrier surface on the foundation, and where the core between the carrier surface on the foundation and the carrier surface of the foundation pile is a cast core, that the fluid for establishing the cast core is a curable casting material, that the curable casting material is let into the cylinder under pressure, that the cylinder is filled with the curable casting material under pressure and a pressure of the fluid is established in the cylinder until the top piston and the bottom piston are situated in their respective positions, and that the curable casting material is cured.
A preferred application of the method relates to a further method for laying a foundation for an existing building structure, said method comprising excavation under an existing foundation, removal of the upper part of an existing foundation pile to provide a carrier surface on a remaining foundation pile and establishment of a core between the carrier surface on the remaining foundation pile and a carrier surface on the remaining foundation, and where the core between the carrier surface on the foundation and the carrier surface of the foundation pile is a cast core, that the fluid is a curable casting material, that the curable casting material is let into the cylinder under pressure, that the cylinder is filled with the curable casting material under pressure until the top piston and the bottom piston are situated in their respective positions, and that the curable casting material is cured.
The present invention also relates to an apparatus comprising a cylinder with a number of pistons, preferably a top piston and a bottom piston, which pistons are telescopically displaceable in relation to one another, preferably that the top piston is telescopically displaceable in relation to the bottom piston, and where at legs one of the pistons is provided with an inlet for a fluid.
In connection with foundation piles, mostly of wood, there may occur rot in the upper part of the foundation pile in connection with a lowering of the groundwater level. This deteriorates or completely removes the carrying capacity of the foundation pile. With a method as discussed above it is possible to re-establish the carrying capacity of the foundation pile.
CH 675 000 describes a method of the above-mentioned type. Prior to removal of an upper part of the foundation pile, a shoring is arranged around the upper part. The shoring extends from the existing foundation down to a part of the foundation pile that will remain after the upper part has been removed. The shoring comprises wooden beams contacting an under side of the existing foundation. Support plates on either side of the remaining foundation pile extend from the wooden beams downward and are fastened to the remaining foundation pile by means of bolts extending between the support plates. A separation plate is displaced perpendicularly in relation to the remaining foundation pile and separates the upper part to be removed from the remaining foundation pile. The upper part is then removed between the support plates. Reinforcements are hammered down into the remaining foundation pile and concrete is cast in the space where the upper part of the foundation pile was previously found.
The method and the apparatus disclosed in the above document involve important drawbacks, however. The initial handling in connection with positioning of wooden beams, support plates and bolts is very comprehensive. Subsequent removal of the upper part of the foundation pile is extremely difficult due to the poor access resulting from support plates and bolts. Final positioning of reinforcements and casting of concrete is also made difficult by support plates and bolts. Besides, it is not possible to establish a support having sufficient carrying capacity due to settling of the cast concrete when the support plates are removed at last. The time that needs to be scheduled to establish the new support is furthermore very important.
SE 346 133 describes a further development compared to the method described in CH 675 000. A telescopic cylinder is provided for adjusting the level of a building or a part of a building. The building or building part may be a foundation or load bars in a building. The building is levelled in relation to the ground or the building part is levelled in relation to a foundation of a building. The adjustment is performed by pumping a fluid into the cylinder. The fluid may be a curable fluid such as cement. The fluid is pumped into the cylinder until the building in relation to the ground or the building part in relation to the foundation of the building has obtained the correct level as desired.
This technique is possible to use if the ground is very solid such as rock which is the ground material of Bromma just outside Stockholm in Sweden where the inventor of the prior art of SE 346 133 is living. Also, if the foundation of the building structure is already at place at the correct level it is easy afterwards to use this prior art to level building parts in relation to the foundation. However, if the ground is not very solid, the technique of SE 346 133 is not possible to use, as the cylinder would just penetrate the ground surface without being able to level the building foundation. If foundation piles is used, also the tecnique of SE 346 133 is not possible to use, because the pressure in the cylinder would just cause the foundation pile to sink and thereby penetrate further down into the ground leaving the foundation pile to be of no use at all.
It is the object of the present invention to disclose a method and to provide an apparatus for use by the method not possessing the above-mentioned many disadvantages and thereby making it possible to use cylinders with fluid under pressure in connection with foundations for building structures which are supported by foundation piles.
This object is obtained by a method that is characterised in that a cylinder is arranged between the carrier surface on the foundation pile and the carrier surface on the foundation with a top piston directed towards the carrier surface on the foundation and a bottom piston directed towards the carrier surface on the foundation pile, that the cylinder is filled with the fluid under pressure until the top piston is in contact with a carrier surface on the foundation and until the bottom piston is in contact with the carrier surface on the foundation pile said pressure established in the cylinder being greater than the pressure by gravity of the building structure on the foundation pile and being smaller than the largest possible load of pressure that the foundation pile is able to assimilate without sinking.
A preferred application of the method is for laying a foundation for an existing building structure, said method comprising excavation under an existing foundation, removal of the upper part of an existing foundation pile to provide a carrier surface on a remaining foundation pile and establishment of a core between the carrier surface on the remaining foundation pile and a carrier surface on the remaining foundation, and is characterised in that a cylinder is arranged between the carrier surface on the remaining foundation pile and the carrier surface on the existing foundation with a top piston directed towards the carrier surface on the existing foundation and a bottom piston directed towards the carrier surface on the remaining foundation pile, that a fluid under pressure is let into the cylinder, that the cylinder is filled with the fluid under pressure until the top piston is in contact with a carrier surface on the existing foundation and until the bottom piston is in contact with the carrier surface on the remaining foundation pile.
An apparatus for use by the method is characterised in that the inlet is provided with a valve, and that the valve is able to adjust the pressure of the fluid being pumped into the cylinder depending on maintaining the level of a building structure abutting the top piston and depending on avoiding sinking of a foundation pile the upper part of which abutting the bottom piston.
The method according to the invention makes it possible first to provide a support that will not settle and, second, to provide a support that will prevent the foundation pile to sink, and, third, to provide this support within a short time. The method is able to use different kinds of curable fluids as cores in the cylinder such as a casting material, e.g. of concrete. In far most cases the fluid is an incompressible fluid.
Non-curable fluids may be applied in order to level e.g. an existing building foundation. Such levelling may take a long time before it has been made sure that a stable situation has been established. Levelling may also take place over a longer period in areas where the foundation means is very unstable. Levelling may take place by positioning a number of cylinders according to the invention under e.g. a building foundation and by frequently adjusting the pressure of the fluid in the cylinder in order to perform the levelling.
In a possible application of the method according to the invention levelling with a non-curable fluid will be replaced by a substitution of the core of a non-curable fluid with a core of a curable fluid as soon as a stable situation has been established. Such application of the method may take place in the same cylinders according to the invention. The non-curable fluid will then be substituted successively by a curable fluid, the curable fluid under the same pressure as the non-curable fluid being let out of the cylinder simultaneously with the curable fluid being let into the cylinder. A curable casting material will constitute a preferred fluid to establish right from the start a core according to the method according to the invention.
The method utilises the possibility of building up a sufficient but not too great a pressure of a fluid in a cylinder and maintaining this pressure in the cylinder. In this manner it is ensured that the support will not settle as the fluid has been cured under pressure and at the same time assure that the foundation pile will not sink during pumping of the fluid into the cylinder and during curing of the fluid under pressure. The pressure may correspond to the pressure that the foundation means, such as a foundation pile, has previously been exposed to, e.g. from a building structure via the foundation of the structure.
In the following, a curable casting material will be used as an example of a fluid for building a core in the cylinder, a building foundation will be used as an example of a structure with a carrier surface, and a foundation pile will be used as an example of a foundation means with a carrier surface. These examples, however, shall not constitute a limitation in the possibilities of exercising the method according to the invention nor a limitation in the possibilities of using the apparatus according to the invention.
The method is very quick in use since it merely requires providing of a carrier surface on the upper part of the foundation pile, perhaps by initial removal of the upper part of the foundation pile, subsequent positioning of cylinder, and finally filling and curing of a casting material. Even if the carrier capacity of the foundation pile is reduced, it has turned out that in many cases it is not necessary to support the foundation while the upper part of the foundation pile is removed and until the new support has been established.
In a preferred embodiment of an apparatus according to the invention the apparatus is characterised in that the cylinder is provided with an inlet and an outlet, that the inlet is provided in the bottom piston, that the outlet is provided in the top piston, and that the inlet is provided with a valve and a manometer.
Providing an inlet for casting mass in the bottom piston or the top piston and an outlet for air in the opposite piston, it is possible with the inlet to fill casting mass into the cylinder and, if required, to replenish the cylinder with casting mass, and it is possible with the outlet to control when the cylinder has been filled with casting mass. The inlet of the preferred embodiment is provided with a valve and a manometer. With a manometer and a valve it is possible to adjust the pressure to a value corresponding e.g. to the pressure to which the foundation pile has previously been exposed, respectively replenish the cylinder with supplemental casting mass if the casting mass shrinks while curing. Among other things it is important that the foundation pile is not exposed to a pressure larger than the pressure to which the foundation pile has previously been exposed since there will then be a risk that the foundation pile may sink.
The cylinder may be provided with a pressure accumulator in order to compensate for any compression or weighing down that may occur, e.g. of a foundation pile when the foundation pile becomes loaded. A pressure accumulator may e.g. consist of one or more rubber elements that will become compressed when the curable casting material is pumped into the cylinder. After the casting material has been pumped into the cylinder, and until the casting material has cured completely, a certain amount of time will pass. Providing a pressure accumulator it is possible to outweigh or at least reduce any pressure reduction in the cylinder resulting from compression or weighing down, e.g. of a foundation pile, during the time span until the casting material has been cured completely.
The cylinder may be lined with a stocking, which may be made impermeable by a moisture-proof medium, a corrosion-restraining medium or other medium such that moisture, corrosive substances or other substances detrimental to the casting material will not be able to penetrate into the cured casting mass. After the casting material has cured, a possibility of removing the cylinder around the cured casting mass may be established. The cylinder may be assembled from several cylinder parts, which contact each other along propellers of the cylinder. Alternatively, the cylinder may be maintained around the casting material after it has cured, without removing the cylinder.
The building structure to be supported may be the foundation of a house, a foundation of a bridge or other kinds of building structures. The foundation means is usually a wooden foundation pile, but it may also be a foundation pile of a different material, in which the upper part of the foundation pile no longer possess sufficient carrier capacity.